Mesh graft and stent for increased flexibility

ABSTRACT

A composite stent-graft tubular prosthesis includes an inner PTFE tubular structure, an outer PTFE tubular structure positioned about the inner PTFE tubular structure and a diametrically deformable stent interposed between the inner and outer PTFE tubular structures. The interposed stent is formed from an elongate wire helically wound with a plurality of longitudinally spaced turns into an open configuration. Each of the turns includes successive aligned upper and lower wave-like peaks. Selective ones of said upper and lower peaks are exposed exteriorly of the outer PTFE structure to render the composite prosthesis longitudinally flexible.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of and claims priority to Ser. No.10/716,639, filed Nov. 19, 2003, which is a continuation of Ser. No.09/571,530 filed May 16, 2000 now U.S. Pat. No. 6,673,103, the contentsof which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to an implantable prosthesisused to repair or replace a body lumen. More particularly, the presentinvention relates to an endoluminal prosthesis including a stent andePTFE graft composite device offering increased compliance andflexibility.

BACKGROUND OF THE INVENTION

An endoluminal prosthesis is a medical device commonly known to be usedin the treatment of diseased blood vessels. An endoluminal prosthesis istypically used to repair, replace, or otherwise correct a damaged bloodvessel. An artery or vein may be diseased in a variety of differentways. The prosthesis may therefore be used to prevent or treat a widevariety of defects such as stenosis of the vessel, thrombosis,occlusion, or an aneurysm.

One type of endoluminal prosthesis used in the repair of diseases invarious body vessels is a stent. A stent is a generally longitudinaltubular device formed of biocompatible material which is useful to openand support various lumens in the body. For example, stents may be usedin the vascular system, urogenital tract and bile duct, as well as in avariety of other applications in the body. Endovascular stents havebecome widely used for the treatment of stenosis, strictures, andaneurysms in various blood vessels. These devices are implanted withinthe vessel to open and/or reinforce collapsing or partially occludedsections of the vessel.

Stents are generally open ended and are radially expandable between agenerally unexpanded insertion diameter and an expanded implantationdiameter which is greater than the unexpanded insertion diameter. Stentsare often flexible in configuration, which allows them to be insertedthrough and conform to tortuous pathways in the blood vessel. The stentis generally inserted in a radially compressed state and expanded eitherthrough a self-expanding mechanism, or through the use of ballooncatheters.

A graft is another type of endoluminal prosthesis which is used torepair and replace various body vessels. Whereas a stent providesstructural support to hold a damaged vessel open, a graft provides anartificial lumen through which blood may flow. Grafts are tubulardevices which may be formed of a variety of material, includingtextiles, and non-textile materials. One type of non-textile materialparticularly suitable for use as an implantable prosthesis ispolytetrafluoroethylene (PTFE). PTFE exhibits superior biocompatibilityand low thrombogenicity, which makes it particularly useful as vasculargraft material in the repair or replacement of blood vessels. Invascular applications, the grafts are manufactured from expanded PTFE(ePTFE) tubes. These tubes have a microporous structure which allowsnatural tissue ingrowth and cell endothelization once implanted in thevascular system. This contributes to long term healing and patency ofthe graft.

It is also known to combine a stent and a graft to form a compositemedical device. Such a composite medical device provides additionalsupport for blood flow through weakened sections of a blood vessel. Inendovascular applications the use of a stent/graft combination isbecoming increasingly important because the combination not onlyeffectively allows the passage of blood therethrough, but also ensuresthe implant will remain open.

Several types of stent/graft inventions are known in the art. U.S. Pat.No. 5,151,105 issued to Kwan-Gett discloses a collapsible textile vesselsleeve with stent members positioned at opposite ends of the sleeve. Thedevice is specifically designed to provide a vessel sleeve that iscollapsible to a very small diameter in order that it may be placed inposition within the abdominal or thoracic aorta by a catheter via thelumen of the femoral artery. Such a procedure obviates the need for amajor surgical intervention, and reduces the risks associated with sucha procedure.

Other stent/graft composite devices using a textile fabric are shown inU.S. Pat. No. 5,628,788, to Pinchuck.

As mentioned above, ePTFE may also be used as graft material instent/graft endoprosthesis. One example of an ePTFE stent/graftcomposite device is shown in U.S. Pat. No. 5,700,285 issued to Myers, etal. Myers discloses a tubular intraluminal graft in the form of atubular diametrically adjustable stent having an interior and exteriortubular covering of porous expanded polytetrafluoroethylene. The tubularcovering surrounds the stent so that the stent is contained duringcontraction and expansion in the delivery process.

Stents are effectively used in combination with grafts as the compositeendoluminal prosthesis allows blood flow through the vessel created bythe graft, while the stent maintains its patency. However, as the graftcovers the stent, it has a tendency to reduce the longitudinalflexibility of the composite device. Longitudinal compliance is ofparticular importance to such stent/graft endoluminal prosthesis as thedevice must be intraluminally delivered through tortuous pathways of ablood vessel to the implantation site where the stent is expanded. Areduction in longitudinal flexibility makes intraluminal delivery moredifficult. Reduction in longitudinal flexibility is particularly evidentwith stents covered by ePTFE, which is not as compliant or flexible astextile materials.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide anendoluminal prosthesis including a stent covered with a graft providingincreased longitudinal flexibility.

It is a further object of the present invention to provide a compositestent/graft providing increased compliance and longitudinal flexibility.

It is a still further object of the present invention to provide acomposite stent/graft having the fluid retention features of an ePTFEgraft without losing the longitudinal flexibility and compliance of astent.

In the efficient attainment of these and other objectives, the presentinvention provides a composite stent-graft tubular prosthesis includingan inner PTFE tubular structure, and an outer PTFE tubular structurepositioned about the inner PTFE tubular structure. A diametricallydeformable stent is interposed between the inner and outer PTFE tubularstructure. The interposed stent is formed from an elongate wirehelically wound with a plurality of longitudinally spaced turns into anopen tubular configuration. Each of the turns include successive upperand lower wave-like peaks wherein selective ones of said upper and lowerpeaks are exposed exteriorly of the outer PTFE structure.

The present invention may further embody a composite stent-graft tubularprosthesis comprising a first PTFE tubular structure with adiametrically deformable stent positioned over said first PTFE tubularstructure. The stent being formed of an elongate helically wound wireformed into an open tubular configuration by a plurality of turns. Thehelically wound wire includes a plurality of transverse generallywave-like undulations there along defining successive upper and lowerpeaks. The tubular prosthesis further includes a second PTFE tubularstructure positioned over said stent. The second PTFE tubular structureincludes a plurality of apertures therethrough, the apertures beingaligned with selective ones of said upper and lower peaks of the stentto expose said upper and lower peaks to thereby enhance longitudinalflexibility of said prosthesis.

A method of making a stent-graft luminal prosthesis of the presentinvention is also disclosed. The method provides for the formation of afirst PTFE tubular structure. A stent is positioned over said first PTFEtubular structure, the stent having a tubular configuration formed of aplurality of turns of a helically wound wire, with each of said turnsincluding successive upper and lower wave-like peaks. A second PTFEtubular structure is then formed over said stent, with said second PTFEtubular structure exposing selective ones of said upper and lowerwave-like peaks through said second PTFE tubular structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective showing, partially in section of a portion of anendoluminal prosthesis of the present invention.

FIG. 2 shows a longitudinal cross-section of the endoluminal prosthesisof FIG. 1 taken through the lines 2—2 thereof.

FIG. 3 shows a longitudinal cross-section of the endoluminal prosthesisof FIG. 1 in a flexed position taken through the line 3—3 thereof.

FIG. 4 shows an enlarged cross-section of a portion of the flexedprosthesis of the present invention.

FIG. 5 is a perspective of a further embodiment of the endoluminalprosthesis of the present invention.

FIG. 6 is a perspective of a stent which may be used in the endoluminalprosthesis of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following is a detailed description of the preferred embodiments ofthe present invention. The description is meant to describe thepreferred embodiments, and is not meant to limit the invention in anyway.

A stent/graft prosthesis 10 of the present invention is shown in FIG. 1.The prosthesis includes a stent 2, an inner tubular layer 4, and anouter tubular layer 6. The stent is positioned between the inner andouter tubular layers.

The stent in the present invention is formed from an elongate wire 12which is helically wound with a plurality of longitudinally spaced turnsinto an open tubular configuration. As partially shown in FIG. 6, astent 2 is of the type which is particularly suited for use in theendoluminal prosthesis of the present invention. The stent 2 is anexpandable tubular member which may be either of the balloon-expanded orself-expanded type. Stents of this type are typically introducedintraluminally into the body, and expanded at the implantation site. Theelongate helically wound wire 12 forming stent 2, defines successiveupper wave-like peaks 14, and lower wave-like peaks 16. The wire 12 iswound into a specific configuration where upper peaks 14 are placedadjacent to lower peaks 16 of the next adjacent winding. While thespecific configuration of the stent 2 shown herein has been found to bepreferable, other stent configurations having open cell expandableconstruction are within the contemplation of the present invention.

Referring now to FIGS. 1 and 2, inner and outer tubular layers, 4 and 6respectively, are shown surrounding stent 2. Layers 4 and 6 are formedof extruded polytetrafluoroethylene (PTFE), as extruded PTFE exhibitssuperior biocompatibility. Further, PTFE is particularly suitable forvascular applications as it exhibits low thrombogenicity. Tubes ofextruded PTFE may also be expanded to form ePTFE tubes. The advantagesof the use of ePTFE materials in forming tubular structures for use asvascular grafts are well known.

PTFE may be extruded as a tube or may be extruded as a sheet or film,and subsequently wrapped around a mandrel to form a tubular structure.While ePTFE tubular structures, whether tubes or wrapped ePTFE sheets,exhibit advantageous biophysical compatibility qualities, suchstructures have a tendency when used in combination with an open stentto reduce the flexibility and longitudinal compliance of the device.This is especially evident where the tubular stent is covered eitherinternally and/or externally with such tubular structures. The presentinvention is intended to create a stent-graft endoluminal prosthesisexhibiting the beneficial physical properties of ePTFE grafts, withoutsignificantly reducing the flexibility of the expandable stent.

In order to increase longitudinal flexibility of stent-graft prosthesis10, outer PTFE tubular layer 6 is constructed so that it exposesexteriorly the upper wave-like peaks 14, and lower wave-like peaks 16 ofstent 2. As mentioned above in a preferred embodiment, the upperwave-like peaks 14 and lower wave-like peaks 16 of the stent are alignedin juxtaposition at various locations along the stent. At such locationsthe outer tubular layer 6 may be found to have a plurality of apertures18. These apertures 18 expose the aligned peaks 14 and 16 exteriorly.The inner layer 4 remains continuous particularly underlying apertures18 so as to maintain a solid tube which functions as a graft.

In the presently described embodiment, all of the stent peaks of a givenstent in the prosthesis are exposed. It is contemplated further thatonly a selected number of aligned peaks may be exposed exteriorly of theendoluminal prosthesis.

The apertures 18 which expose the peaks may be formed into a variety ofshapes. As particularly shown in FIG. 1, the apertures 18 are formed ascircular holes through which the successive peaks 14 and 16 are exposed.However other aperture configurations may also be employed.

The stent/graft composite device of the present invention is constructedby initially forming a first inner tubular layer 4. As mentioned above,tubular layer 4 maybe formed from an extruded tube or a formed extrudedsheet by processes well known in the art. Stent 2 is then positionedover the inner PTFE tubular layer 4. Stent 2 has a tubular configurationformed of a plurality of turns of a helically wound wire, each of saidturns including successive upper and lower wave-like peaks. The woundwire is formed such that peaks 14 and 16 are placed in alignedjuxtaposition. A second outer PTFE tubular layer 6 is then formed overstent 2. The second outer tubular layer is then modified so as to exposeselective aligned upper and lower wave-like peaks through the secondPTFE tubular layer 6.

In a preferred embodiment of the present invention, the stent/graftprosthesis includes an open wall stent 12 of tubular constructionsupported between an inner PTFE tubular layer 4, and an outer PTFEtubular layer 6. The inner PTFE tubular layer 4 may be bonded to theouter PTFE tubular layer through the spaces 15 in the open wall of thestent 2. The bonding may be effectuated with the use of an adhesive, orby adhering the layers together without an adhesive. Bonding of the PTFElayers without an adhesive may take place by such methods as laminating,or sintering of the prosthesis. Furthermore, the stent may be adhered tothe inner PTFE tubular layer, the outer PTFE tubular layer, or both.Similarly, such adherence may take place with or without the use of anadhesive.

Once the stent 2 is positioned between layers 4 and 6, a cutting tool(not shown) may be used to expose upper and lower wave-like peaks of thestent exteriorly of the outer PTFE tubular structure. The cutting toolmay be used to cut apertures in the outer tubular layer 6 so as toexpose the peaks of the stent. Some cutting tools which may be usedinclude a razor blade and a laser. The prosthesis may be sintered priorto exposing the stent peaks, or after said exposure step.

The increased longitudinal flexibility and compliance of the prosthesismay be clearly illustrated with reference to FIGS. 2–4.

As described above the successive upper peaks 14 are juxtaposed withrespect to the lower peaks 16. The juxtapositioning of the successivepeaks creates a flexion similar to a joint. To further optimizeflexibility, the endoluminal prosthesis reduces any movement restrictionas between peaks 14 and 16, as the juxtaposed peaks of the stent areexposed exteriorly of the outer PTFE structure. FIG. 4 shows such alongitudinal flexion in the endoluminal prosthesis. Such longitudinalflexion may be the result of intraluminal delivery of the device throughthe tortuous blood vessel system. As the juxtaposed peaks are exposedexteriorly of the outer PTFE structure, the exposed peaks have atendency to project externally away from the first tubular structure,creating a space 20 between the stent and the inner tubular structurewhen longitudinally flexed. The exposure of the peaks enables the stentto exhibit uncovered flexibility as the stent is not restricted fromexhibiting movement between the wire windings as would be the case ifthe stent were completely covered.

As set forth in the above preferred embodiment, longitudinal complianceof the device may be achieved by placing apertures in the outer layerover the aligned peaks of the stent. However, other techniques may beemployed to increase the longitudinal compliance of the covered stent.Referring now to FIG. 5, a composite stent/graft prosthesis 10′ isshown. Prosthesis 10′ is substantially similar to stent/graft prosthesis10 of FIG. 1, having a stent 2′, an inner tubular layer 4′ and an outertubular layer 6′. The stent peaks 14 and 16 may be exteriorly exposed toincrease the longitudinal flexibility of the prosthesis 10′.

In the embodiment of FIG. 5, the peaks 14′ may be exposed by accessingthe stent 2′ through the outer layer 6′. A cutting tool (not shown) maybe used to cut slits 22′ in the outer tubular structure through whichthe stent peaks 14′ are exposed. The stent peaks are subsequently pulledthrough said slits, and the PTFE comprising the outer tubular structureis subsequently tucked underneath the stent peaks at area 24′. Thisembodiment provides flexibility in a similar manner because the stentpeaks are similarly exposed and the construction allows a full range ofmotion of the stent peaks. While exposure of only one peak 14′ is shownin FIG. 5, it may be appreciated that the exposure of other peaks 14′and 16′ may be provided.

1. A method of forming a stent-graft prosthesis comprising the step of:forming a first PTFE tubular structure; positioning a stent over saidfirst PTFE tubular structure, said stent having a tubular configurationformed of a plurality of turns of a helically wound wire, each of saidturns including successive upper and lower wave-like peaks; forming asecond PTFE tubular structure over said stent; and exposing selectiveones of said upper and lower wave-like peaks through said second PTFEtubular structure, wherein exposing includes placing a plurality ofslits through said second PTFE tubular structure at a location alignedwith said selective upper and lower peaks of said stent; and extendingsaid upper and lower peaks of said stent through said slits.
 2. A methodof claim 1 further including the step of adheringly securing said firstPTFE tubular stent to said second PTFE tubular structure through spacesbetween said wound wire.
 3. A method of claim 2 wherein said extendingstep includes: lifting said selective upper and lower peaks; tucking aportion of said second PTFE tubular structure adjacent said slit, undersaid upper and lower peaks.
 4. A method of claim 2 wherein said placingstep includes: cutting said slits using a cutting tool.
 5. A method ofclaim 2 wherein said placing step includes: laser burning said slitsthrough said second PTFE tubular structure.
 6. A method of claim 2wherein said exposing step includes: forming said second PTFE tubularstructure with a plurality of apertures, said apertures being at alocation adjacent said selective upper and lower peaks.
 7. A method ofclaim 1 wherein said second PTFE tubular structure is sintered prior tosaid exposing step.
 8. A method of claim 1 wherein said second PTFEtubular structure is sintered subsequent to said exposing step.